SMPTE

...or Society of Motion Picture and Television Engineers, is an industry standard timecode used for audio and video production and editing. It is by far the most accurate time-indexing standard and can be used for delivering professional quality production and portability. Most equipment utilizing SMPTE (pronounced simp-tee) can be quite expensive, since it was designed for video professionalsand production houses, and has been out of reach from consumers for quite a long time. But in the last few years, amateurs and consumers have been able to get easy access to software that allows them to do video and audio production at home with professional quality in a non-linear editing setup using SMPTE, since it is now the widely adopted standard in production. Not to mention that almost every consumer grade Digital Video camcorder now has SMPTE built it as well. Examples of some popular software packages are Adobe Premiere, Adobe Audition (formerly Syntrillium Software's Cool Edit Pro), Macromedia Director, and a number of other software packages since the hardware for chaining devices for SMPTE synchronization often embedded in a MIDI, serial or IEEE-1394 protocol. I will go into some details here on how SMPTE is implemented on an analog system.

Video recordings on analog VCR tapes use a control track along the edge of the tape to be able to align the heads and tell the recorder exactly where each video frame starts and ends. This is simply a modulated analog signal of 30 pulses per second across the edge of tape, which can determine the point of the tape decimally, in the following format hours:minutes:seconds.decimal (hh:mm:ss.ddd). In a linear-editing setup this control track is can be prone to error and can introduce skips of a few frames between the audio and video or between clips because a VCR sometimes cannot pick up on the control track while the motors are speeding up during a pre-roll.

Instead of working with this error-prone system, the Society needed an easier and more accurate way to encode and identify the time within the medium they were working with. They developed a system that uses the video frames themselves for time-indexing instead of a decimal format. The SMPTE displayed timecode is hours:minutes:seconds:frames (hh:mm:ss:ff) Video in this day and age commonly use the following framerates:

The big difference between the NTSC 30fps versus NTSC 29.97fps is that while the NTSC standard defines the framerate as 30fps, the color system used in NTSC televisions doesn't run at exactly 30fps, but runs at 29.97fps introducing a discrepancy of 00:00:03:18 every hour of recording. QXZ's writeup of timecode explains quite nicely how drop frame encoding corrects this difference.

The two primary ways of encoding a digital SMPTE timecode onto an analog video recording are Longitudinal Time Code (LTC) and Vertical Interval Time Code (VITC). The LTC is recorded along an audio track and has the advantage of being able to be added or edited independently of the video, but also has the disadvantage of possibly sacrificing your existing audio track depending on the equipment used to record the digital signal, and where the track is located on the tape. Also since LTC is an audio signal, it can suffer from attenuation during copying and dubbing. VITC, on the other hand is recorded onto the picture itself (visible in the first couple rasterscanlines, top-left side, of a video frame along with any closed captioning (top-right) signals). The advantage of VITC is that it does not affect the audio in any way and will survive any copying intact, but the disadvantage is that it must be encoded at the time of the recording and cannot be edited very easily without the use of some dedicated encoding equipment and some painstaking work.